Valve actuator

ABSTRACT

A fluid pressure operated actuator assembly comprising a tubular body ( 110 ) having a wall, with an interior surface and an exterior surface and enclosing a main passage ( 112 ) which extends generally parallel to a longitudinal axis of the tubular body, an actuator ( 118 ) located in and movable along the main passage, a first direction chamber ( 138   a ) formed between the wall of the tubular body and the actuator, and at least one second direction chamber ( 138   b, c ) formed between the tubular body and the actuator, wherein the assembly is configured such that when the pressure of fluid in the first direction chamber exceeds the pressure of fluid in the or each second direction chamber by a predetermined amount, the pressure of fluid in the first direction chamber exerts a force on the actuator which acts to push the actuator in a first direction relative to the tubular body, and when the pressure of fluid in the or at least one of the second direction chamber(s) exceeds the pressure of fluid in the first direction chamber by a predetermined amount, the pressure of fluid in the second direction chamber(s) exerts a force on the actuator which acts to push the actuator in a second direction relative to the tubular body, characterised in that the exterior surface of the tubular body is provided with a first port ( 140   a ) which communicates with a passage ( 139   a ) extending through the wall of the tubular body from the first port to the first direction chamber, a second port ( 140   b ) which communicates with a passage ( 139   b ) extending through the wall of the tubular body from the second port to the or one of the second direction chamber(s), 
     and a third port ( 140   c ) which communicates with a passage ( 139   c ) extending through the wall of the tubular body from the third port to the or another one of the second direction chamber(s), the first port lying on a first plane, the second port lying on a second plane and the third port lying on a third plane, the first plane, second plane and third plane being generally parallel to one another and the first plane lying between the second plane and the third plane.

DESCRIPTION OF INVENTION

The present invention relates to a valve actuator, particularly, but notexclusively, for use in actuating a rotatable valve member mounted in atubular used in oil or gas drilling and/or production.

The drilling of a borehole or well is typically carried out using asteel pipe known as a drill pipe or drill string with a drill bit on thelowermost end. The drill string comprises a series of tubular sections,which are connected end to end.

The entire drill string may be rotated using a rotary table, or using anover-ground drilling motor mounted on top of the drill pipe, typicallyknown as a ‘top-drive’, or the drill bit may be rotated independently ofthe drill string using a fluid powered motor or motors mounted in thedrill string just above the drill bit. As drilling progresses, a flow ofmud is used to carry the debris created by the drilling process out ofthe borehole. Mud is pumped down the drill string to pass through thedrill bit, and returns to the surface via the annular space between theouter diameter of the drill string and the borehole (generally referredto as the annulus). The mud flow also serves to cool the drill bit, andto pressurise the borehole, thus substantially preventing inflow offluids from formations penetrated by the drill string from entering intothe borehole. Mud is a very broad drilling term and in this context itis used to describe any fluid or fluid mixture used during drilling andcovers a broad spectrum from air, nitrogen, misted fluids in air ornitrogen, foamed fluids with air or nitrogen, aerated or nitrifiedfluids to heavily weighted mixtures of oil and or water with solidparticles.

Significant pressure is required to drive the mud along this flow path,and to achieve this, the mud is typically pumped into the drill stringusing one or more positive displacement pumps which are connected to thetop of the drill string via a pipe and manifold.

Whilst the main mud flow into the well bore is achieved by pumping mudinto a main, axial, passage at the very top end of the drill string, itis also known to provide the drill string with a side passage whichextends into the main passage from a port provided in the side of thedrill string, so that mud can be pumped into the main passage at analternative location to the top of the drill string.

For example, as drilling progresses, and the bore hole becomes deeperand deeper, it is necessary to increase the length of the drill string,and this is typically achieved by disengaging the top drive from the topof the drill string, adding a new section of tubing to the drill string,engaging the top drive with the free end of the new tubing section, andthen recommencing drilling. It will, therefore, be appreciated thatpumping of mud down the drill string ceases during this process.

Stopping mud flow in the middle of the drilling process is problematicfor a number of reasons, and it has been proposed to facilitatecontinuous pumping of mud through the drill string by the provision of aside passage, typically in each section of drill string. This means thatmud can be pumped into the drill string via the side passage whilst thetop of the drill string is closed, the top drive disconnected and thenew section of drill string being connected.

In one such system, disclosed in U.S. Pat. No. 2,158,356, at the top ofeach section of drill string, there is provided a side passage which isclosed using a plug, and a valve member which is pivotable between afirst position in which the side passage is closed whilst the mainpassage of the drill string is open, and a second position in which theside passage is open whilst the main passage is closed. During drilling,the valve is retained in the first position, but when it is time toincrease the length of the drill string, the plug is removed from theside passage, and a hose, which extends from the pump, connected to theside passage, and a valve in the hose opened so that pumping of mud intothe drill string via the side passage commences. A valve in the mainhose from the pump to the top of the drill string is then closed, andthe pressure of the mud at the side passage causes the valve member tomove from the first position to the second position, and hence to closethe main passage of the drill string.

The main hose is then disconnected, the new section of tubing mounted onthe drill string, and the main hose connected to the top of the newsection. The valve in the main hose is opened so that pumping of mudinto the top of the drill string is recommenced, and the valve in thehose to the side passage closed. The resulting pressure of mud enteringthe top of the drill string causes the valve member to return to itsfirst position, which allows the hose to be removed from the sidepassage, without substantial leakage of mud from the drill string.

The side passage may then be sealed permanently, for example by weldingor screwing a plug into the side passage, before this section of drillstring is lowered into the well.

This process is commonly referred to as continuous circulation drilling.

In other similar systems, instead of providing a single valve memberwhich is operable to close either the side passage or the main passageof the drill string, it is known to provide two separate valve members—amain valve member which is operable to close the main passage, and anauxiliary valve member which is operable to close the side passage. Inthis case, the separate valve members may each have its own actuationmechanism, for example as disclosed in WO2010/046653.

A further alternative arrangement in which the actuator for the mainvalve member is combined with the auxiliary valve member is disclosed inWO2012/085597. This arrangement is illustrated in FIGS. 1a and 1 b.

In this arrangement, the main valve member 16 comprises a ball which ismounted in the main passage 12 of the drill string 10, and which isrotatable about an axis generally perpendicular to the longitudinal axisof the drill string, between an open position in which flow of fluidalong the main passage 12 is permitted, and a closed position in whichit prevents flow of fluid along the main passage 12. Rotation of theball 16 between the open position and the closed position is achievedusing a tubular actuator 18, which is also mounted within the mainpassage 12 of the drill string 10, coaxially with the drill string 10.The actuator 18 is connected to the ball 16 such that sliding movementof the 18 in the drill string 10 causes the ball 16 to move between theclosed position and the open position. The actuator 18 also acts toblock or unblock the side passage 14 as it slides along the drillstring, and is configured to open the side passage 14 when the mainvalve 16 is in the closed position, and to close the side passage 14when the main valve 16 is in the open position.

The actuator 18 is hydraulically actuated by mean of an actuationchamber 38 which is provided between the actuator 18 and a lining 10 aprovided in the wall of the drill string 10. This is best illustrated inFIG. 1c , and simply comprises an annular space between the two parts18, 10 a. Two ports 40 a, 40 b are provided through the drill string 10into this chamber 38, one at each end of the chamber 38. The first port40 a is closest to a second end 18 b of the actuator 18 (nearest themain valve member 16).

The chamber 38 is divided into two by a seal 41 which is mounted on theexterior surface of the actuator 18. In one embodiment, the seal 41comprises 2 O-rings. The seal 41 substantially prevents flow of fluidbetween the two parts of the chamber 38 whilst permitting the actuator18 to slide inside the drill string 10. The seal 41 ensures that flow ofpressurised fluid into this chamber 38 via the first port 40 a causesthe actuator 18 to move towards the main valve member 16, whilst flow ofpressurised fluid into the actuation chamber 38 via the second port 40 bacts in the opposite direction to counterbalance the effect ofpressurised fluid at the first port 40 a. The actuator 18 therefore actsas a double acting piston with one pressure port 40 a to move theactuator 18 towards the main valve member 16 and one pressure port tomove the actuator 18 away from the main valve member 16. In other wordsthe actuator 18 is operated by means of a pressure differential acrossthe first and second ports 40 a, 40 b.

FIG. 1a illustrates the actuator 18 when supply of pressurised fluid tothe port 40 b has pushed it away from the main valve member 16, so thatthe actuator 18 closes the side port 14, whilst FIG. 1b illustrates thesleeve 18 when supply of pressurised fluid to the port 40 a has pushedit towards the main valve member 16, thus opening the side port 14.

The mechanism whereby the actuator sleeve 18 is connected to the ball 16so that sliding movement of the actuator sleeve 18 causes the ball 16 torotate is described fully in WO2012/085597. Various similar arrangementsare also known from GB 2 413 373, U.S. Pat. No. 3,236,255, GB 1 416 085,U.S. Pat. No. 3,703,193 and U.S. Pat. No. 3,871,447.

These arrangements may also be used to control flow of fluid through aside passage in what is known as a “pump in sub”, which is used in theevent of an emergency, for example to facilitate the provision ofadditional mud pressure required to control a sudden surge in well-borepressure due to fluid inflow from a formation penetrated by the wellentering the well in what is known as a “kick”.

This invention relates to an alternative configuration of actuatorassembly suitable for use in such a valve arrangement, where operationof the valve is achieved by the sliding of an actuator sleeve relativeto the drill string.

According to a first aspect of the invention we provide a fluid pressureoperated actuator assembly comprising a tubular body having a wall, withan interior surface and an exterior surface and enclosing a main passagewhich extends generally parallel to a longitudinal axis of the tubularbody, an actuator located in and movable along the main passage, a firstdirection chamber formed between the wall of the tubular body and theactuator, and at least one second direction chamber formed between thetubular body and the actuator, wherein the assembly is configured suchthat when the pressure of fluid in the first direction chamber exceedsthe pressure of fluid in the or each second direction chamber by apredetermined amount, the pressure of fluid in the first directionchamber exerts a force on the actuator which acts to push the actuatorin a first direction relative to the tubular body, and when the pressureof fluid in the or at least one of the second direction chamber(s)exceeds the pressure of fluid in the first direction chamber by apredetermined amount, the pressure of fluid in the second directionchamber(s) exerts a force on the actuator which acts to push theactuator in a second direction relative to the tubular body,characterised in that the exterior surface of the tubular body isprovided with a first port which communicates with a passage extendingthrough the wall of the tubular body from the first port to the firstdirection chamber, a second port which communicates with a passageextending through the wall of the tubular body from the second port tothe or one of the second direction chamber(s), and a third port whichcommunicates with a passage extending through the wall of the tubularbody from the third port to the or another one of the second directionchamber(s), the first port lying on a first plane, the second port lyingon a second plane and the third port lying on a third plane, the firstplane, second plane and third plane being generally parallel to oneanother and the first plane lying between the second plane and the thirdplane.

In one embodiment, the longitudinal axis of the tubular body extendsgenerally normal to the first plane, second plane and third plane.

In one embodiment, one or both of the first and second directions is/aregenerally parallel to the longitudinal axis of the tubular body.

In one embodiment, the first direction is generally opposite to thesecond direction.

In one embodiment, the actuator is connected to a main valve member insuch a way that movement of the actuator in the first direction andsecond direction causes the valve member to move. In this embodiment,the main valve member may be movable between a closed position in whichthe main valve member closes the main passage of the tubular body and anopen position in which the main passage of the tubular body is open. Themovement of the main valve member caused by the movement of the actuatorin the first direction and second direction may comprise rotation.

In one embodiment, the main valve member moves to the closed positionwhen the actuator moves in the first direction and to the open positionwhen the actuator moves in the second direction.

The main valve member may comprise a ball valve member.

The actuator may be connected to valve member by means of a track andpin arrangement whereby a pin extends from on of the valve member oractuator into a slot or groove provided in the other of the valve memberor actuator, the pin moving along the slot or groove as the actuatorslides in the tubular body and the valve member rotates.

In one embodiment, the tubular body is provided with a side passagewhich extends through the wall of the tubular body from the exterior ofthe tubular body into the main passage, and the actuator is movablebetween a closed position in which the actuator substantially preventsflow of fluid along the side passage, and an open position in which flowof fluid along the side passage is permitted. In this case, movement ofthe actuator in the first direction may bring the actuator into the openposition, and movement of the actuator in the second direction may bringthe actuator into the closed position. Where a main valve member is alsoprovided as described above, movement of the actuator in the firstdirection may bring the actuator into the open position and the mainvalve member into the closed position, whilst movement of the actuatorin the second direction brings the actuator into the closed position,and the main valve member into the open position.

The passage from the third port may connect to the passage from thesecond port into the or one of the second direction chamber(s).

The first direction chamber and the or each second direction chamber maybe formed in a space between an exterior surface of the actuator and aninterior surface of the wall of the tubular body. This space may extendaround the entire perimeter of the actuator. This space may be dividedinto the first direction chamber and second direction chamber by meansof a seal which substantially prevents flow of fluid between thechambers whilst allowing the actuator to move along the main passage ofthe tubular body. This space may be divided into the first directionchamber and two second direction chambers by means of a seal arrangementwhich substantially prevents flow of fluid between the chambers whilstallowing the actuator to move along the main passage of the tubularbody. The first direction chamber may be located between the two seconddirection chambers. In this case, the passages from the first port,second port and third port into their respective chambers may extendthrough the tubular body generally perpendicular to its longitudinalaxis. Alternatively, at least one of the passages from the first port,second port and third port into their respective chambers may extendthrough the tubular body generally at an angle of less than 90° to itslongitudinal axis.

In one embodiment, the actuator assembly is configured such that if thepressure in the first direction chamber equals the pressure in the orboth second direction chamber(s), there is no net force acting on theactuator, if the pressure in the first direction exceeds the pressure inthe or both the second direction chamber(s), there is a net force actingon the actuator pushing the actuator in the first direction, and if thepressure in the first direction chamber is less than the pressure in theor either one of the second direction chamber(s), there is a net forceacting on the actuator pushing the actuator the second direction.

In one embodiment, the actuator assembly is configured such that whenthe pressure in the first direction chamber equals the pressure in theor both second direction chamber(s), there is a net force acting on theactuator.

In this case, the actuator assembly may be configured such that this netforce tends to push the actuator in the second direction.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the following figures of which;

FIGS. 2a and 2b show a longitudinal cross-section through a portion ofone embodiment of actuator assembly according to the invention, theactuator having been moved in the second direction in FIG. 2a and in thefirst direction in FIG. 2 b,

FIGS. 3a and 3b show a longitudinal cross-section through a portion ofan alternative embodiment of actuator assembly according to theinvention, the actuator having been moved in the second direction inFIG. 3a and in the first direction in FIG. 3b , AND

FIGS. 4a and 4b show a longitudinal cross-section through a portion ofan alternative embodiment of actuator assembly according to theinvention, the actuator having been moved in the second direction inFIG. 4a and in the first direction in FIG. 4 b.

Referring now to FIGS. 2a and 2b , there is shown a fluid pressureoperated actuator assembly comprising a tubular body 110 having a wallenclosing a main passage 112 which extends generally parallel to alongitudinal axis of the tubular body 110, an actuator 118 located inand movable along the main passage 112, a first direction chamber 138 aand a second direction chamber 138 b formed between the wall of thetubular body 110 and the actuator 118. The tubular body 110 may be partof a drill string or may comprise a sub for mounting in a drill string.

In this embodiment, both the tubular body 110 and actuator 118 aretubular with a generally circular cross-section. The first directionchamber 138 a and the second direction chamber 138 b are formed in anannular space around the actuator 118 between an exterior surface of theactuator 118 and an interior surface of the tubular body 110. This spaceis divided into the first direction chamber 138 a and second directionchamber 138 b by means of a seal 141 which substantially prevents flowof fluid between the chambers 138 a 138 b. Two further seals 118 a, 130a are provided between the exterior surface of the actuator 118 and theinterior surface of the tubular body 110, one at each end of the annularspace.

In this embodiment, the seals 118 a, 130 a, and 141 each comprise a pairof generally circular O-rings which are located in circumferentialgrooves around the exterior surface of the actuator 118. It should beappreciated, however, that the invention is not restricted to the use ofthis particular type of seal, and any other type of seal whichsubstantially prevents flow of fluid between the actuator 118 and thetubular body 110 whilst allowing the actuator 118 to slide in thetubular body 110, could be used instead. The seals could equally bemounted on the tubular body 110 rather than on the actuator 118.

The tubular body 110 is provided with a first port 140 a whichcommunicates with a first control passage 139 a extending through thewall of the tubular body 110 from the first port 140 a to the firstdirection chamber 138 a, a second port 140 b which communicates with asecond control passage 139 b extending through the wall of the tubularbody 110 from the second port 140 b to the second direction chamber 138b and a third port 140 c which communicates with a third control passage139 c extending through the wall of the tubular body 110 from the thirdport 140 c to the second control passage 139 b. In this example, thefirst and second control passages 139 a, 139 b extend through the wallof the tubular body generally perpendicular to its longitudinal axis.The third passage 139 c is inclined at angle of less than 45° to thelongitudinal axis of the tubular body. In this example, the first andsecond control passages 139 a, 139 b are co-planar and so both can beseen in the cross-sections illustrated in FIGS. 2a and 2b . The thirdcontrol passage 139 c necessarily extends along a different plane and sois shown in dashed lines in these Figures.

The first, second and third ports 140 a, 140 b, 140 c are spaced alongthe longitudinal axis of the tubular body 110 so that if the first port140 a is considered to lie on a first imaginary plane, the second port140 b on a second imaginary plane and the third port 140 c on a thirdimaginary plane, the first plane, second plane and third plane beinggenerally parallel to one another and generally normal to thelongitudinal axis of the tubular body 110, the first plane lies betweenthe second plane and the third plane.

The actuator assembly is configured such that when the pressure of fluidin the first direction chamber 138 a exceeds the pressure of fluid inthe second direction chamber 138 b, the pressure of fluid in the firstdirection chamber 138 a exerts a force on the actuator 118 which acts topush the actuator 118 in a first direction along the main passage 112 inthe tubular body 110, and when the pressure of fluid in the seconddirection chamber 138 b exceeds the pressure of fluid in the firstdirection chamber 138 a, the pressure of fluid in the second directionchamber 138 b exerts a force on the actuator 118 which acts to push theactuator 118 in a second, opposite, direction along the main passage 112in the tubular body 110.

In this example, this is achieved by providing the interior of thetubular body 110 with a portion of increased internal diameter 110 a. Ateither end of this portion 110 a, the interior surface of the tubularbody 110 forms a shoulder 110 b, 110 c where the internal diameter ofthe tubular body 110 decreases slightly. The actuator 118 issubstantially longer than the portion of increased internal diameter 110a and the outer diameter of the actuator 118 is less than the internaldiameter of the tubular body 110 either side of the portion of increasedinternal diameter 110 a. The first direction and second directionchambers 138 a, 138 b are formed between the actuator 118 and theportion of increased internal diameter 110 a, and the seal 141 extendsoutwardly of the exterior surface of the actuator 118 to engage with theinterior surface of increased internal diameter portion 110 a of thetubular body 110. The first direction chamber 138 a is thus formedbetween the exterior surface of the actuator 118, the first shoulder 110b, part of the increased internal diameter portion of the tubular body110, and the seal 141. Similarly, the second direction chamber 138 b isformed between the exterior surface of the actuator 118, the secondshoulder 110 c, part of the increased internal diameter portion of thetubular body 110, and the seal 141.

When pressurised fluid is supplied to the first port 140 a, the fluidpressure pushes the seal 141 away from the first shoulder 110 b toincrease the volume of the first direction chamber 138 a. The actuator118 is therefore pushed in the first direction. Similarly, whenpressurised fluid is supplied to the second or third ports 140 b, 140 c,the fluid pressure in the second direction chamber 138 b pushes the seal141 away from the second shoulder 110 c to increase the volume of thesecond direction chamber 138 b. The actuator 118 is thus pushed in thesecond direction. The actuator 118 therefore acts as a double actingpiston with a first port 140 a to move the actuator 118 in a firstdirection along the main passage 112 in the tubular body 110 (in thisexample to the left in FIGS. 2a and 2b ) and a second port 140 b or athird port 140 c to move the sleeve 18 in a second direction along themain passage 112 in the tubular body 110 (in this example to the rightin FIGS. 2a and 2b ).

It should be appreciated that this embodiment differs from the prior artactuator described in WO2012/085597, and GB 2 413 373, for examples, byvirtue of the provision of the third port 140 c. The third port 140 cmay be advantageous as it may assist in preventing unwanted movement ofthe actuator 118 when the exterior of the tubular body 110 is exposed toa pressure differential. This is particularly important where thetubular body is portion of a drill string, or a sub mounted in a drillstring, and the drill string is used in managed pressure drilling (MPD).

In a conventional drilling fluid system, only one drilling fluidgradient exists, and differential pressure between two points in thedrill string can be described by the hydrostatic head and any frictionalforces associated with a dynamic system. Managed pressure drilling (MPD)is a style of drilling in which the bottom hole pressure (BHP) ismaintained through various methods including fluid level maintenance,effective fluid density manipulation, applied back pressure, andpotentially combinations of these and other practices. The use of arotating control device (RCD) is becoming increasingly common inoffshore applications to meet the demands of MPD wells in deep waterenvironments.

An RCD clamps around the drill string to main fluid pressuredifferential in the annulus around the drill string (typically there ishigher pressure below the RCD), whilst allowing the drill string torotate as required for drilling. The RCD is intended as a means ofisolating one part of the wellbore from another during drillingoperations, and can be inserted at any point in a riser string,depending on the application, for the purpose of dual gradient drilling(DGD) or applying back pressure to the riser annulus, or other purposes.

The RCD therefore creates an irregularity or discontinuity in theoverall pressure profile of the well, which, in practical terms, maymean that as the drill string is inserted into the well, a point on thedrill string may experience a sudden increase in pressure by 500 psi ormore having traveled only 6 inches or less. This differential pressuremay act from below a drill string element, i.e. the area of highpressure being lower than the area of low pressure. Differentialpressure may also act from above, however, for example if the riser andRCD is configured more toward well control.

The valve assembly described in WO2012/085597 is reliable inconventional single fluid gradient environments, as the distance betweenthe first and second ports 40 a, 40 b is relatively short. This meansthat as the portion of the drill string containing these ports 40 a, 40b is advanced into the well, any pressure differential across the portsas a result of the pressure gradient in the annulus is negligible, andis not sufficient to move the actuator 18. This may not be the case,however, if the drill string were to pass through a discontinuity in thepressure gradient such as one introduced by an RCD. Where an RCD isused, there may exist a point in the riser where, when the portion ofthe drill string including the ports 40 a, 40 b passes through,differential pressure may be seen from above or below, which exceeds theactuating pressure of the actuator 18. This may, therefore, result inunintended movement of the actuating sleeve 18. The provision of thethird port 140 c may prevent this as will be described below.

To achieve this, in use, the actuator 118 should be arranged such thatits default or rest position is as illustrated in FIG. 2b , and isadopted by virtue of the supply of pressurised fluid to the secondand/or third ports 140 b, 140 c. As the tubular body 110 passes througha pressure discontinuity such as one introduced by an RCD, if theportion of the tubular body 110 shown on the left hand side of FIGS. 2aand 2b encounters the high pressure first, the second port 140 b isexposed to high pressure (the high pressure also being communicated tothe third port 140 c), whilst the first port 140 a is at low pressure.The high pressure at the second and third ports 140 b, 140 c will act tomaintain the actuator 118 in its rest/default position. As the passageof the tubular body 110 through the pressure discontinuity continues,the first port 140 a will then also be exposed to the high pressure, butas this is balanced by the same high pressure at the second and thirdports 140 b, 140 c the actuator 118 will not move. As the pressurediscontinuity passes, the pressure at all three ports 140 a, 140 b, 140c is substantially equal.

Similarly, if the portion of the tubular body 110 shown on the righthand side of FIGS. 2a and 2b encounters the high pressure first, thethird port 140 c is exposed to high pressure (which is also communicatedto the second port 140 b), whilst the first port 140 a is at lowpressure. The high pressure at the second and third ports 140 b, 140 cwill act to maintain the actuator 118 in its rest/default position. Asthe passage of the tubular body 110 through the pressure discontinuitycontinues, the first port 140 a will then also be exposed to the highpressure, but as this is balanced by the same high pressure at thesecond and third port 140 c, the actuator 118 will still not move.

Thus, the actuator 118 will not be moved from its default or restposition by the pressure discontinuity, whichever end of the tubularbody 110 is exposed to the high pressure first, and the actuatorassembly can therefore cope with pressure differential from above andbelow without unintended actuation.

Although not essential to the invention, in this embodiment, the tubularbody 110 is provided with a side passage 114 which extends from theexterior of the body 110 into the main passage 112. The actuator 118 isprovided with a further seal 130 b which provide a substantially fluidtight seal between the actuator 118 and the tubular body 110 to ensurethat, when the actuator is in a closed position (illustrated in FIG. 2b), the actuator substantially prevents flow of fluid along the sidepassage 114.

In this example, this further seal 130 b comprises two seals each ofwhich is a generally circular O-ring which are located incircumferential grooves around the exterior surface of the actuator 118.The further seal 130 b and the seal 130 a provided to contain fluidpressure in the first direction chamber 138 a are spaced such that whenthe actuator 118 is in the closed position, the side port 114 liesbetween the two seals 130 a, 130 b. Again, it should be appreciated thatthe invention is not restricted to the use of this particular type ofseal, and any other type of seal which substantially prevents flow offluid between the actuator 118 and the tubular body 110 whilst allowingthe actuator 118 to slide in the tubular body 110, could be usedinstead.

In this embodiment, movement of the actuator 118 from the closedposition to the open position comprises movement in the first direction,which movement is, as described above, achieved by supply of pressurisedfluid to the first port 140 a. Correspondingly, movement of the actuator118 from the open position to the closed position comprises movement inthe second direction, which movement is, as described above, achieved bysupply of pressurised fluid to the second or third port 140 b, 140 c.This means that, when the actuator 118 is in the closed position, it ismaintained in that position even when the tubular body 110 passesthrough a pressure discontinuity such as created by an RCD in a managedpressure drilling situation. Thus, leakage of fluid out of the mainpassage 112 of the tubular body 110 via the side port 114 when thetubular body passes through a pressure discontinuity should be avoided.

FIG. 2a illustrates the actuator 118 when supply of pressurised fluid tothe first port 140 a has pushed it in the first direction, thus openingthe side port 114, whilst FIG. 2b illustrates the actuator 118 whensupply of pressurised fluid to the second or third port 140 b, 140 c haspushed it in the second direction, so that the actuator 118 closes theside port 114.

It will be appreciated, however, that the actuator assembly couldequally be configured such that the opposite is true—i.e. movement ofthe actuator 118 from the closed position to the open position comprisesmovement in the second direction etc, so that the actuator 118 isbrought to or maintained in the open position when it passes through apressure discontinuity.

In one embodiment the actuator 118 is connected to a main valve member(not shown) in such a way that movement of the actuator 118 in the firstdirection and second direction causes the main valve member to move. Themain valve member may be movable between a closed position in which themain valve member closes the main passage 112 of the tubular body 110and an open position in which the main passage 112 of the tubular body110 is open. The movement of the main valve member caused by themovement of the actuator 118 in the first direction and second directionmay comprise rotation, and the main valve member may be a ball valve.

In one embodiment, the actuator 118 is connected to valve member bymeans of a track and pin arrangement whereby a pin extends from one ofthe valve member or actuator into a slot or groove provided in the otherof the valve member or actuator, the pin moving along the slot or grooveas the actuator 118 slides in the tubular body 110 and the valve memberrotates. Various possible mechanisms whereby the actuator 118 could beconnected to the main valve member so that sliding movement of theactuator 118 causes the main valve member to rotate are described in WO2012/085597, GB 2 413 373, U.S. Pat. No. 3,236,255, GB 1 416 085, U.S.Pat. No. 3,703,193 and U.S. Pat. No. 3,871,447.

In a preferred embodiment, the main valve member moves to its closedposition when the actuator 118 moves in the first direction, whichmovement is, as described above, achieved by supply of pressurised fluidto the first port 140 a. Correspondingly, the main valve moves to itsopen position when the actuator 118 moves in the second direction, whichmovement is, as described above, achieved by supply of pressurised fluidto the second or third port 140 b, 140 c. This means that, the mainvalve member is brought to or maintained in its open position when thetubular body 110 passes through a pressure discontinuity such as createdby an RCD in a managed pressure drilling situation. Thus, unintentionalblocking of the main passage 112 of the tubular body 110 by the mainvalve member when the tubular body 110 passes through a pressurediscontinuity should be avoided. This is particularly advantageous whenthe assembly is used in a drill string in managed pressure drilling, asclosing of the main valve stops the flow of drilling fluid down thedrill string, and this could lead to potential sticking and well controlissues, and is likely to force a trip out of the well at significantcost.

Not only is it possible for the actuator 118 to either facilitate theopening or closing of a side port 114 through the tubular body 110 orcontrol the opening or closing of a main valve member, it is possiblefor the actuator 118 to do both. In other words, both a side port 114and main valve member as described above, may be provided. In this case,the assembly is advantageously configured such that movement of theactuator 118 in the first direction brings the actuator 118 into theopen position and the main valve member into the closed position, whilstmovement of the actuator 118 in the second direction brings the actuator118 into the closed position, and the main valve member into the openposition.

An alternative embodiment of actuator assembly is illustrated in FIGS.3a and 3b . In this embodiment, two second direction chambers 138 b, 138c are provided, the second port 138 b connecting the exterior of thetubular body 110 with the first second direction chamber 138 b and thethird port 138 c connecting the exterior of the tubular body 110 withthe second second direction chamber 138 c. The first direction chamber138 a is located between the two second direction chambers 130 b, 138 c.In this embodiment, the passages from the first port 140 a, second port140 b, and third port 140 c into their respective chambers 138 a, 138 b,138 c extend through the tubular body 110 generally perpendicular to itslongitudinal axis.

Again, in this embodiment, both the tubular body 110 and actuator 118are tubular with a generally circular cross-section. The first directionchamber 138 a and the second direction chambers 138 b, 138 c are formedin an annular space around the actuator 118 between an exterior surfaceof the actuator 118 and an interior surface of the tubular body 110.This space is divided into the first direction chamber 138 a and twosecond direction chambers 138 b, 138 d by means of three seals 141, 143,145 which substantially prevent flow of fluid between the chambers 138 a138 b, 138 c. Again, two further seals 118 a, 130 a are provided betweenthe exterior surface of the actuator 118 and the interior surface of thetubular body 110, one at each end of the annular space.

As before, in this embodiment, the seals 118 a, 130 a, 141, 143, 145each comprise a pair of generally circular O-rings which are located intwo circumferential grooves around the exterior surface of the actuator118. It should be appreciated, however, that this invention is notrestricted to the use of this particular type of seal, and any othertype of seal which substantially prevents flow of fluid from thechambers 138 a, 138 b, 138 c whilst allowing the actuator 118 to slidein the tubular body 110, could be used instead. The seals could equallybe mounted on the tubular body 110 rather than on the actuator 118.

Again, the actuator assembly is configured such that when the pressureof fluid in the first direction chamber 138 a exceeds the pressure offluid both of the second direction chambers 138 b, 138 c, the pressureof fluid in the first direction chamber 138 a exerts a force on theactuator 118 which acts to push the actuator 118 in a first directionalong the main passage 112 in the tubular body 110, and when thepressure of fluid in either of the second direction chambers 138 b, 138c exceeds the pressure of fluid in the first direction chamber 138 a,the pressure of fluid in the second direction chamber in question 138 b,138 c exerts a force on the actuator 118 which acts to push the actuator118 in a second, opposite, direction along the main passage 112 in thetubular body 110.

In this example, this is achieved by providing the interior of thetubular body 110 with two portions of increased internal diameter 110 a,110 a′. At either end of these portions 110 a, 110 a′, the interiorsurface of the tubular body 110 forms a shoulder 110 b, 110 c, 110 d,110 e where the internal diameter of the tubular body 110 decreasesslightly. The actuator 118 is substantially longer than both theportions of increased internal diameter 110 a, 110 a′ together, and theouter diameter of the actuator 118 is less than the internal diameter ofthe tubular body 110 either side of the portions of increased internaldiameter 110 a, 110 a′. The first direction and second directionchambers 138 a, 138 b, 138 c are formed between the actuator 118 and theportions of increased internal diameter 110 a, 110 a′, and two of theseals 141, 145 extend outwardly of the exterior surface of the actuator118 to engage with the interior surface of increased internal diameterportions 110 a, 110 a′ of the tubular body 110, one being located ineach portion of increased internal diameter 110 a, 110 a′. The middleseal 143 engages with a portion of the internal surface of the tubularwall 110 between the two portions of increased internal diameter 110 a,110 a′.

As in the embodiment illustrated in FIGS. 2a and 2b , the firstdirection chamber 138 a is formed between the exterior surface of theactuator 118, the first shoulder 110 b, the middle seal 143, part of thefirst increased internal diameter portion 110 a of the tubular body 110,and the seal 141. Similarly, the first second direction chamber 138 b isformed between the exterior surface of the actuator 118, the end seal118 a, the second shoulder 110 c, part of the first increased internaldiameter portion 110 a of the tubular body 110, and the seal 141. Thesecond direction chamber 138 c is formed between the exterior surface ofthe actuator 118, the middle seal 143, the third shoulder 110 d, part ofthe second increased internal diameter portion 110 a′ of the tubularbody 110, and the seal 145.

When pressurised fluid is supplied to the first port 140 a, the fluidpressure pushes the seal 141 away from the first shoulder 110 b toincrease the volume of the first direction chamber 138 a. The actuator118 is therefore pushed in the first direction. Similarly, whenpressurised fluid is supplied to the second port 140 b, the fluidpressure in the first second direction chamber 138 b pushes the seal 141away from the second shoulder 110 c to increase the volume of the seconddirection chamber 138 b. The actuator 118 is thus pushed in the seconddirection. Also, when pressurised fluid is supplied to the third port140 a, the fluid pressure in the second second direction chamber 138 cpushes the seal 145 away from the third shoulder 110 d to increase thevolume of the second second direction chamber 138 c. The actuator 118therefore acts as a double acting piston with a first port 140 a to movethe actuator 118 in a first direction along the main passage 112 in thetubular body 110 (in this example to the left in FIGS. 3a and 3b ) and asecond port 140 b or a third port 140 c to move the sleeve 18 in asecond direction along the main passage 112 in the tubular body 110 (inthis example to the right in FIGS. 3a and 3b ). In other words, theeffect of fluid pressure at the first, second and third ports 140 a, 140b, 140 c is exactly the same as in the embodiment described in relationto FIGS. 2a and 2b , and any or all of the additional features of theearlier embodiment can also be applied to this embodiment.

A further alternative embodiment of the invention is illustrated inFIGS. 4a and 4b . This embodiment is very similar to the embodimentdescribed with reference to FIGS. 3a and 3b , in that it too has asecond second direction chamber 138 c—the difference lies in relation tothe order of the chambers 138 a, 138 b, 138 c. Whilst in the FIG. 3a /3b embodiment, the first direction chamber 138 a is located between thetwo second direction chambers 138 b, 138 c, in this alternativeembodiment, the two second direction chambers 138 b, 138 c are next toone another. So that the first port 140 a can lie on an imaginary planewhich is between the imaginary plane on which the second port 140 b andthe third port 140 c lie, the control passage 139 a to the firstdirection chamber 138 a and the control passage 139 c to the secondsecond direction chamber 138 c extend diagonally through the wall of thetubular body 110. In this example, the control passage 139 b to thefirst second direction chamber 138 b extends through the tubular body110 generally perpendicular to its longitudinal axis.

In this example, this arrangement of the chambers is achieved byproviding the interior of the tubular body 110 with three portions ofincreased internal diameter 110 a, 110 a′, 110 a″. At either end of eachof these portions 110 a, 110 a′, 110 a″, the interior surface of thetubular body 110 forms a shoulder 110 b, 110 c, 110 d, 110 e where theinternal diameter of the tubular body 110 changes slightly. The internaldiameter of the tubular body 110 in the first and third increaseddiameter portions 110 a, 110 a″, is less than the internal diameter ofthe tubular body 110 in the second increased diameter portion 110 a′.The second increased diameter portion 110 a′ lies directly between thefirst and third increased internal diameter portions 110 a, 110 a″.

The actuator 118 is substantially longer than all the portions ofincreased internal diameter 110 a, 110 a′, 110 a″ together, and theouter diameter of the actuator 118 is less than the internal diameter ofthe tubular body 110 either side of the portions of increased internaldiameter 110 a, 110 a′, 110 a″. The first direction and second directionchambers 138 a, 138 b, 138 c are formed between the actuator 118 and theportions of increased internal diameter 110 a, 110 a′, and the threeseals 141, 143, 145 extend outwardly of the exterior surface of theactuator 118 to engage with the interior surface of increased internaldiameter portions 110 a, 110 a′, 110 a″ of the tubular body 110, onebeing located in each portion of increased internal diameter 110 a, 110a′, 110 a″. The seal 141 engages with the first increased diameterportion 110 a, the middle seal 143 engages with the second increasedinternal diameter 110 a′, and the final seal 145 engages with the thirdincreased diameter portion 110 a″.

In contrast to the arrangement shown in FIGS. 3a and 3b , the firstdirection chamber 138 a is formed between the exterior surface of theactuator 118, the middle seal 143, part of the third increased internaldiameter portion 110 a″ of the tubular body 110, the end shoulder 110 eand the seal 145. Similarly, the first second direction chamber 138 b isformed between the exterior surface of the actuator 118, the shoulder110 c, the end seal 118 a, part of the first increased internal diameterportion 110 a of the tubular body 110, and the first seal 141. Thesecond second direction chamber 138 c is formed between the exteriorsurface of the actuator 118, the shoulder 110 b, the first seal 141,part of the second increased internal diameter portion 110 a′ of thetubular body 110, and the middle seal 143.

When pressurised fluid is supplied to the first port 140 a, the fluidpressure pushes the seal 143 away from the first shoulder 110 d toincrease the volume of the first direction chamber 138 a. The actuator118 is therefore pushed in the first direction. Similarly, whenpressurised fluid is supplied to the second port 140 b, the fluidpressure in the first second direction chamber 138 b pushes the seal 141away from the shoulder 110 c to increase the volume of the seconddirection chamber 138 b. The actuator 118 is thus pushed in the seconddirection. Also, when pressurised fluid is supplied to the third port140 a, the fluid pressure in the second second direction chamber 138 cpushes the seal 143 away from the shoulder 110 b to increase the volumeof the second second direction chamber 138 c. The actuator 118 thereforeacts as a double acting piston with a first port 140 a to move theactuator 118 in a first direction along the main passage 112 in thetubular body 110 (in this example to the left in FIGS. 4a and 4b ) and asecond port 140 b or a third port 140 c to move the sleeve 18 in asecond direction along the main passage 112 in the tubular body 110 (inthis example to the right in FIGS. 4a and 4b ). In other words, theeffect of fluid pressure at the first, second and third ports 140 a, 140b, 140 c is exactly the same as in the embodiment described in relationto FIGS. 2a and 2b , and any or all of the additional features of theearlier embodiment can also be applied to this embodiment.

As the tubular body 110 passes through a pressure discontinuity such asone introduced by an RCD, if the portion of the tubular body 110 shownon the left hand side of FIG. 3a, 3b, 4a or 4 b encounters the highpressure first, the second port 140 b is exposed to high pressure whilstthe first and third ports 140 a, 140 c are at low pressure. The highpressure at the second port 140 b will only act to maintain the actuator118 in its rest/default position. As the passage of the tubular body 110through the pressure discontinuity continues, the first port 140 a willthen also be exposed to the high pressure, but as this is balanced bythe same high pressure at the second port 140 b, the actuator 118 willnot move. Finally, the third port 140 c will also be exposed to the highpressure, so the pressure at all three ports 140 a, 140 b, 140 c issubstantially equal.

Similarly, if the portion of the tubular body 110 shown on the righthand side of FIGS. 3a, 3b, 4a and 4b encounters the high pressure first,the third port 140 c is exposed to high pressure whilst the first andsecond ports 140 a, 140 b are at low pressure. The high pressure at thethird port 140 c will only act to maintain the actuator 118 in itsrest/default position. As the passage of the tubular body 110 throughthe pressure discontinuity continues, the first port 140 a will thenalso be exposed to the high pressure, but as this is balanced by thesame high pressure at the third port 140 c, the actuator 118 will stillnot move. Finally, the second port 140 b will also be exposed to thehigh pressure, so the pressure at all three ports 140 a, 140 b, 140 c issubstantially equal.

The embodiments described in relation to FIGS. 3a, 3b, 4a and 4b has anadvantage over the embodiments described in relation to FIGS. 2a and 2bwhen passed through a device such as an RCD which seals around thetubular body 110 to maintain a pressure discontinuity either side of theRCD. Where the embodiment illustrated in FIGS. 2a and 2b is used, whenone of the second port 140 b or third port 140 c is exposed to the highpressure at one side of the RCD, if the RCD seals do not close the otherof the second port 140 b or third port 140 c, these ports provide a flowpath for flow of fluid across the RCD. This cannot occur when the thirdport 140 c connects to a second second direction chamber 138 c.

In the embodiments of the invention described above, the actuatorassembly is configured such that the first direction and seconddirection chamber(s) 138 a, 138 b, 138 c are pressure balanced. Thismeans that if the pressure in the first direction chamber 138 a equalsthe pressure in the or both second direction chamber(s) 138 b, 138 c,there is no net force acting on the actuator 118, if the pressure in thefirst direction exceeds the pressure in the or both the second directionchamber(s), there is a net force acting on the actuator 118 pushing theactuator 118 in the first direction, and if the pressure in the firstdirection chamber 138 a is less than the pressure in the or either oneof the second direction chamber(s) 138 b, 138 c, there is a net forceacting on the actuator 118 pushing the actuator 118 in the seconddirection. This is achieved by configuring the first direction andsecond direction chamber(s) 138 a, 138 b, 138 c in such a way that thecross-sectional area of the first direction chamber 138 a perpendicularto the first direction is equal to the cross-sectional area of the oreach second direction chamber 138 b, 138 c perpendicular to the seconddirection.

This is realised in the embodiment illustrated in FIGS. 2a and 2b byensuring that the shoulder 110 c which partly encloses the seconddirection chamber 138 b has substantially the same depth as the shoulder110 b which partly encloses the first direction chamber 138 a. This isrealised in the embodiment illustrated in FIGS. 2a, and 2b by ensuringthat the shoulder 110 c which partly encloses the first second directionchamber 138 b, the shoulder 110 b which partly encloses the firstdirection chamber 138 a, and the shoulder 110 d which partly enclosesthe second second direction chamber 138 c are substantially equal indepth.

This need not be the case, however, and the actuator assembly mayconfigured in an non-pressure balanced fashion so that when the pressurein the first direction chamber 138 a equals the pressure in the or bothsecond direction chamber(s), there is a net force acting on the actuator118.

In this case, it is preferable for this net force to push the actuator118 in the second direction. If this is the case, it will be appreciatedthat to move the actuator 118 in the first direction, it will benecessary to increase the fluid pressure in the first direction chamber138 a relative to the fluid pressure in the or both of the seconddirection chamber(s) 138 b, 138 c so that the fluid pressure in thefirst direction chamber 138 a exceeds the pressure in the or both of thesecond direction chamber(s) 138 b, 138 c by a predetermined margin.Moreover, once the actuator 118 has been moved in the first direction,it will be pushed back in the second direction once the fluid pressurein the first direction chamber 138 a falls below the level set by thatpredetermined margin, even if it still exceeds the pressure in the orboth of the second direction chamber(s) 138 b, 138 c.

This can be achieved by configuring the first direction and seconddirection chamber(s) 138 a, 138 b, 138 c in such a way that thecross-sectional area of the first direction chamber 138 a perpendicularto the first direction is less than the cross-sectional area of the oreach second direction chamber 138 b, 138 c perpendicular to the seconddirection.

In the embodiment shown in FIGS. 2a and 2b one way this relativedecrease of the cross-sectional area of the first direction chamber 138a with respect to the cross-sectional area of the second directionchamber 138 b could be realised is by increasing the depth of theshoulder 110 c which partly encloses the second direction chamber 138 b(by decreasing the internal diameter of the tubular body 110 on the sideof the shoulder 110 c outside the increased internal diameter portion110 a and decreasing the outer diameter of the actuator 118 on thesecond direction chamber 138 b side of the seal 141 between the twochambers 138 a, 138 b). In the embodiment illustrated FIGS. 3a and 3b ,one way this relative decrease of the cross-sectional area of the firstdirection chamber 138 a with respect to the cross-sectional area of thesecond direction chambers 138 b, 138 c could be realised is byincreasing the depth of the shoulder 110 c which partly encloses thefirst second direction chamber 138 b (by decreasing the internaldiameter of the tubular body 110 on the side of the shoulder 110 coutside the increased internal diameter portion 110 a and decreasing theouter diameter of the actuator 118 on the second direction chamber 138 bside of the seal 141 between the two chambers 138 a, 138 b) andincreasing the depth of shoulder 110 d which partly encloses the secondsecond direction chamber 138 c (by increasing the internal diameter ofthe second increased internal diameter portion 110 a′ of tubular body).

When used in this specification and claims, the terms “comprises” and“comprising” and variations thereof mean that the specified features,steps or integers are included. The terms are not to be interpreted toexclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may, separately, or in any combination of such features, be utilised forrealising the invention in diverse forms thereof.

1-26. (canceled)
 27. A fluid pressure operated actuator assemblycomprising: a tubular body having a wall, with an interior surface andan exterior surface and enclosing a main passage which extends generallyparallel to a longitudinal axis of the tubular body; an actuator locatedin and movable along the main passage; a first direction chamber formedbetween the wall of the tubular body and the actuator; and at least onesecond direction chamber formed between the tubular body and theactuator, wherein the assembly is configured such that when the pressureof fluid in the first direction chamber exceeds the pressure of fluid inthe or each second direction chamber by a predetermined amount, thepressure of fluid in the first direction chamber exerts a force on theactuator which acts to push the actuator in a first direction relativeto the tubular body, and when the pressure of fluid in the or at leastone of the second direction chamber(s) exceeds the pressure of fluid inthe first direction chamber by a predetermined amount, the pressure offluid in the second direction chamber(s) exerts a force on the actuatorwhich acts to push the actuator in a second direction relative to thetubular body, and wherein the exterior surface of the tubular body isprovided with a first port which communicates with a passage extendingthrough the wall of the tubular body from the first port to the firstdirection chamber, a second port which communicates with a passageextending through the wall of the tubular body from the second port tothe or one of the second direction chamber(s), and a third port whichcommunicates with a passage extending through the wall of the tubularbody from the third port to the or another one of the second directionchamber(s), the first port lying on a first plane, the second port lyingon a second plane and the third port lying on a third plane, the firstplane, second plane and third plane being generally parallel to oneanother and the first plane lying between the second plane and the thirdplane.
 28. The fluid pressure operated actuator assembly according toclaim 27, wherein the longitudinal axis of the tubular body extendsgenerally normal to the first plane, second plane and third plane. 29.The fluid pressure operated actuator assembly according to claim 27,wherein one or both of the first and second directions is/are generallyparallel to the longitudinal axis of the tubular body.
 30. The fluidpressure operated actuator assembly according to claim 27, wherein thefirst direction is generally opposite to the second direction.
 31. Thefluid pressure operated actuator assembly according to claim 27, whereinthe actuator is connected to a main valve member in such a way thatmovement of the actuator in the first direction and second directioncauses the valve member to move.
 32. The fluid pressure operatedactuator assembly according to claim 31, wherein the main valve memberis movable between a closed position in which the main valve membercloses the main passage of the tubular body and an open position inwhich the main passage of the tubular body is open.
 33. The fluidpressure operated actuator assembly according to claim 31, wherein themain valve member moves to the closed position when the actuator movesin the first direction and to the open position when the actuator movesin the second direction.
 34. The fluid pressure operated actuatorassembly according to claim 31, wherein the actuator is connected to amain valve member by means of a track and pin arrangement whereby a pinextends from on of the valve member or actuator into a slot or grooveprovided in the other of the valve member or actuator, the pin movingalong the slot or groove as the actuator slides in the tubular body andthe valve member rotates.
 35. The fluid pressure operated actuatorassembly according to claim 27, wherein the tubular body is providedwith a side passage which extends through the wall of the tubular bodyfrom the exterior of the tubular body into the main passage, and theactuator is movable between a closed position in which the actuatorsubstantially prevents flow of fluid along the side passage, and an openposition in which flow of fluid along the side passage is permitted. 36.The fluid pressure operated actuator assembly according to claim 35,wherein movement of the actuator in the first direction brings theactuator into the open position, and movement of the actuator in thesecond direction brings the actuator into the closed position.
 37. Thefluid pressure operated actuator assembly according to claim 27, whereinthe passage from the third port connects to the passage from the secondport into the or one of the second direction chamber(s).
 38. The fluidpressure operated actuator assembly according to claim 27, wherein thefirst direction chamber and the or each second direction chamber areformed in a space between an exterior surface of the actuator and aninterior surface of the wall of the tubular body.
 39. The fluid pressureoperated actuator assembly according to claim 38, wherein this space isdivided into the first direction chamber and second direction chamber bymeans of a seal which substantially prevents flow of fluid between thechambers whilst allowing the actuator to move along the main passage ofthe tubular body.
 40. The fluid pressure operated actuator assemblyaccording to claim 38, wherein this space is divided into the firstdirection chamber and two second direction chambers by means of a sealarrangement which substantially prevents flow of fluid between thechambers whilst allowing the actuator to move along the main passage ofthe tubular body.
 41. The fluid pressure operated actuator assemblyaccording to claim 40, wherein the first direction chamber locatedbetween the two second direction chambers.
 42. The fluid pressureoperated actuator assembly according to claim 40, wherein the passagesfrom the first port, second port and third port into their respectivechamber extend through the tubular body generally perpendicular to itslongitudinal axis.
 43. The fluid pressure operated actuator assemblyaccording to claim 40, wherein at least one of the passages from thefirst port, second port and third port into their respective chamberextends through the tubular body generally at an angle of less than 90°to its longitudinal axis.
 44. The fluid pressure operated actuatorassembly according to claim 27, wherein the actuator assembly isconfigured such that if the pressure in the first direction chamberequals the pressure in the or both second direction chamber(s), there isno net force acting on the actuator, if the pressure in the firstdirection exceeds the pressure in the or both the second directionchamber(s), there is a net force acting on the actuator pushing theactuator in the first direction, and if the pressure in the firstdirection chamber is less than the pressure in the or either one of thesecond direction chamber(s), there is a net force acting on the actuatorpushing the actuator the second direction.
 45. The fluid pressureoperated actuator assembly according to claim 27, wherein the actuatorassembly is configured such that when the pressure in the firstdirection chamber equals the pressure in the or both second directionchamber(s), there is a net force acting on the actuator.
 46. The fluidpressure operated actuator assembly according to claim 45, wherein theactuator assembly is configured such that this net force tends to pushthe actuator in the second direction.